alpha-synuclein and benzyloxycarbonylleucyl-leucyl-leucine-aldehyde

The aim of the present study was to examine the effects of proteasome inhibitor (PI)‑induced autophagy on PC12 cells overexpressing A53T mutant α‑synuclein (α‑syn) by detecting alterations in the levels of microtubule‑associated protein 1A/1B light chain (LC3)+ autophagosomes and the lysotracker‑positive autolysosomes using immunofluorescence, the expression of LC3‑II using western blot analysis and the morphology of PC12 cells using transmission electron microscopy. It was found that the addition of MG132 (500 nmol/l) significantly increased the number of autophagosomes and autolysosomes and upregulated the expression of LC3‑II. The autophagy inhibitor 3‑methyladenine (3‑MA) completely inhibited the autophagy induced by MG132 (500 nmol/l). The autophagy enhancer trehalose significantly increased the number of autophagosomes and autolysosomes and improved the protein level of LC3‑II induced by MG132. To examine the effect of PI‑induced autophagy on the degradation of A53T mutant α‑syn, the expression of α‑syn was detected by western blot analysis. It was revealed that MG132 increased the expression of A53T α‑syn and trehalose counteracted the increase of A53T α‑syn induced by MG132. Combined inhibition of 3‑MA and PI significantly increased the accumulation of A53T α‑syn as compared with treatment using either single agent. In addition, combination of MG132 (500 nmol/l) with trehalose (50 mmol/l) or 3‑MA (2 mmol/l) markedly decreased the cell viability as compared with treatment using either single agent individually as demonstrated using a 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide assay. These results suggest that the PI, MG132, could induce autophagy in PC12 cells overexpressing A53T mutant α‑syn and this autophagy could be completely inhibited by 3‑MA, indicating that PI‑induced autophagy is mediated by the upregulation of the macroautophagy class III PI3K pathway. PI‑induced autophagy may act as a compensatory degradation system for degradation of A53T α‑syn when the ubiquitin‑proteasome system is impaired. Autophagy activation may directly contribute to the survival of PC12 cells treated with proteasome inhibitors. The present study may assist in illuminating the association between PI and autophagy in the pathogenesis of Parkinson's disease.

Topics: Adenine; alpha-Synuclein; Animals; Autophagy; Cell Death; Gene Expression; Leupeptins; Mutation; PC12 Cells; Proteasome Inhibitors; Rats; TOR Serine-Threonine Kinases

Gene multiplications or point mutations in alpha (α)-synuclein are associated with familial and sporadic Parkinson's disease (PD). An increase in copper (Cu) levels has been reported in the cerebrospinal fluid and blood of PD patients, while occupational exposure to Cu has been suggested to augment the risk to develop PD. We aimed to elucidate the mechanisms by which α-synuclein and Cu regulate dopaminergic cell death. Short-term overexpression of wild type (WT) or mutant A53T α-synuclein had no toxic effect in human dopaminergic cells and primary midbrain cultures, but it exerted a synergistic effect on Cu-induced cell death. Cell death induced by Cu was potentiated by overexpression of the Cu transporter protein 1 (Ctr1) and depletion of intracellular glutathione (GSH) indicating that the toxic effects of Cu are linked to alterations in its intracellular homeostasis. Using the redox sensor roGFP, we demonstrated that Cu-induced oxidative stress was primarily localized in the cytosol and not in the mitochondria. However, α-synuclein overexpression had no effect on Cu-induced oxidative stress. WT or A53T α-synuclein overexpression exacerbated Cu toxicity in dopaminergic and yeast cells in the absence of α-synuclein aggregation. Cu increased autophagic flux and protein ubiquitination. Impairment of autophagy by overexpression of a dominant negative Atg5 form or inhibition of the ubiquitin/proteasome system (UPS) with MG132 enhanced Cu-induced cell death. However, only inhibition of the UPS stimulated the synergistic toxic effects of Cu and α-synuclein overexpression. Our results demonstrate that α-synuclein stimulates Cu toxicity in dopaminergic cells independent from its aggregation via modulation of protein degradation pathways.

Topics: alpha-Synuclein; Animals; Apoptosis; Caspases; Cells, Cultured; Copper; Cysteine Proteinase Inhibitors; Dopaminergic Neurons; Embryo, Mammalian; Gene Expression Regulation; Humans; Leupeptins; Mesencephalon; Mutation; Neuroblastoma; Proteolysis; Rats; Rats, Sprague-Dawley; Signal Transduction; Time Factors; Tyrosine 3-Monooxygenase

Parkinson disease (PD) is the second most common neurodegenerative disease, and it cannot be completely cured by current medications. In this study, DJ-1 protein was administrated into medial forebrain bundle of PD model rats those had been microinjected with 6-hydroxydopamine (6-OHDA) or MG-132. We found that DJ-1 protein could reduce apomorphine-induced rotations, inhibit reduction of dopamine contents and tyrosine hydroxylase levels in the striatum, and decrease dopaminergic neuron death in the substantia nigra. In 6-OHDA lesioned rats, uncoupling protein-4, uncoupling protein-5 and superoxide dismutase-2 (SOD2) mRNA and SOD2 protein were increased when DJ-1 protein was co-injected. Simultaneously, administration of DJ-1 protein reduced α-synuclein and hypoxia-inducible factor 1α mRNA and α-synuclein protein in MG-132 lesioned rats. Therefore, DJ-1 protein protected dopaminergic neurons in two PD model rats by increasing antioxidant capacity and inhibiting α-synuclein expression.

Topics: alpha-Synuclein; Animals; Antiparkinson Agents; Apomorphine; Corpus Striatum; Dopamine; Dopaminergic Neurons; Drug Evaluation, Preclinical; Humans; Hypoxia-Inducible Factor 1, alpha Subunit; Intracellular Signaling Peptides and Proteins; Ion Channels; Leupeptins; Male; Microinjections; Mitochondrial Membrane Transport Proteins; Mitochondrial Proteins; Mitochondrial Uncoupling Proteins; Motor Activity; Nerve Tissue Proteins; Neuroprotective Agents; Oncogene Proteins; Oxidative Stress; Oxidopamine; Parkinsonian Disorders; Protein Deglycase DJ-1; Rats; Rats, Sprague-Dawley; Substantia Nigra; Superoxide Dismutase; Tyrosine 3-Monooxygenase

α-Synuclein (a-Syn) is a major component of fibrillar aggregates in Lewy bodies (LBs), a characteristic hallmark of Parkinson disease. Almost 90% of a-Syn deposited in LBs is phosphorylated at Ser-129. However, the role of Ser-129-phosphorylated a-Syn in the biogenesis of LBs remains unclear. Here, we investigated the metabolism of Ser-129-phosphorylated a-Syn. In SH-SY5Y cells, inhibition of protein phosphatase 2A/1 by okadaic acid, and inhibition of the proteasome pathway by MG132 or lactacystin accumulated Ser-129-phosphorylated a-Syn. However, these inhibitions did not alter the amounts of total a-Syn within the observation time. Inhibition of the autophagy-lysosome pathway by 3-methyladenine or chloroquine accumulated Ser-129-phosphorylated a-Syn in parallel to total a-Syn during longer incubations. Experiments using cycloheximide showed that Ser-129-phosphorylated a-Syn diminished rapidly (t(½) = 54.9 ± 6.4 min), in contrast to the stably expressed total a-Syn. The short half-life of Ser-129-phosphorylated a-Syn was blocked by MG132 to a greater extent than okadaic acid. In rat primary cortical neurons, either MG132, lactacystin, or okadaic acid accumulated Ser-129-phosphorylated a-Syn. Additionally, we did not find that phosphorylated a-Syn was ubiquitinated in the presence of proteasome inhibitors. These data show that Ser-129-phosphorylated a-Syn is targeted to the proteasome pathway in a ubiquitin-independent manner, in addition to undergoing dephosphorylation. The proteasome pathway may play a role in the biogenesis of Ser-129-phosphorylated a-Syn-rich LBs.

Topics: Acetylcysteine; alpha-Synuclein; Animals; Cell Line, Tumor; Cerebral Cortex; Cycloheximide; Cysteine Proteinase Inhibitors; Humans; Leupeptins; Lewy Bodies; Neurons; Okadaic Acid; Parkinson Disease; Phosphorylation; Proteasome Endopeptidase Complex; Proteasome Inhibitors; Protein Phosphatase 1; Protein Phosphatase 2; Protein Synthesis Inhibitors; Rabbits; Ubiquitin

alpha-Synuclein is the major building block of cytoplasmic inclusions in neurodegenerative disorders named synucleinopathies. These inclusion bodies often contain the small heat shock protein alphaB-crystallin and the microtubule-associated protein tau. Oxidative modification of alpha-synuclein has been linked to fibril formation, and alpha-synuclein aggregation may induce the fibrillization of tau. To study alpha-synuclein aggregate formation, we have engineered oligodendroglial cells (OLN-93 cells) to stably express the longest human isoform of tau and wild-type alpha-synuclein or the A53T alpha-synuclein mutation. Under normal growth conditions, small punctuated alpha-synuclein aggregates were formed, which were more abundant in cells expressing the A53T mutation. After exposure to oxidative stress, protein inclusions were enlarged and were positive for thioflavin S, but the solubility of alpha-synuclein was not altered. Oxidative stress followed by proteasomal inhibition caused the occurrence of larger thioflavin S-positive inclusions, immunoreactive for tau and alphaB-crystallin, thus resembling glial cell inclusion bodies. Furthermore, this double stress situation led to a decrease in alpha-synuclein solubility, and alphaB-crystallin and HSP90 were present in the insoluble fraction. The formation and recruitment of tau to thioflavin S-positive protein aggregates in OLN-93 cells only expressing tau in the absence of alpha-synuclein, either after oxidative or proteasomal stress or both, was not observable. The data indicate that oxidatively modified alpha-synuclein is degraded by the proteasome and that it plays a pro-aggregatory role for tau in this cell culture model system.

Topics: alpha-Crystallin B Chain; alpha-Synuclein; Animals; Cysteine Proteinase Inhibitors; Humans; Hydrogen Peroxide; Hydrolysis; Inclusion Bodies; Leupeptins; Oligodendroglia; Oxidants; Oxidative Stress; Proteasome Endopeptidase Complex; Proteasome Inhibitors; Protein Isoforms; tau Proteins

Parkinson disease (PD) involves progressive neurodegeneration, including loss of dopamine (DA) neurons from the substantia nigra. Select genes associated with rare familial forms of PD function in cellular pathways, such as the ubiquitin-proteasome system (UPS), involved in protein degradation. The misfolding and accumulation of proteins, such as alpha-synuclein, into inclusions termed Lewy Bodies represents a clinical hallmark of PD. Given the predominance of sporadic PD among patient populations, environmental toxins may induce the disease, although their nature is largely unknown. Thus, an unmet challenge surrounds the discovery of causal or contributory neurotoxic factors that could account for the prevalence of sporadic PD. Bacteria within the order Actinomycetales are renowned for their robust production of secondary metabolites and might represent unidentified sources of environmental exposures. Among these, the aerobic genera, Streptomyces, produce natural proteasome inhibitors that block protein degradation and may potentially damage DA neurons. Here we demonstrate that a metabolite produced by a common soil bacterium, S. venezuelae, caused DA neurodegeneration in the nematode, Caenorhabditis elegans, which increased as animals aged. This metabolite, which disrupts UPS function, caused gradual degeneration of all neuronal classes examined, however DA neurons were particularly vulnerable to exposure. The presence of DA exacerbated toxicity because neurodegeneration was attenuated in mutant nematodes depleted for tyrosine hydroxylase (TH), the rate-limiting enzyme in DA production. Strikingly, this factor caused dose-dependent death of human SH-SY5Y neuroblastoma cells, a dopaminergic line. Efforts to purify the toxic activity revealed that it is a highly stable, lipophilic, and chemically unique small molecule. Evidence of a robust neurotoxic factor that selectively impacts neuronal survival in a progressive yet moderate manner is consistent with the etiology of age-associated neurodegenerative diseases. Collectively, these data suggest the potential for exposures to the metabolites of specific common soil bacteria to possibly represent a contributory environmental component to PD.

Topics: Actinomycetales; Aging; alpha-Synuclein; Animals; Caenorhabditis elegans; Cell Line, Tumor; Culture Media, Conditioned; Dopamine; Environment; Humans; Leupeptins; Neurodegenerative Diseases; Protease Inhibitors; Protein Denaturation; Soil Microbiology; Streptomyces; Substantia Nigra

Parkinson's disease (PD) is a neurologic disorder characterized by dopaminergic cell death in the substantia nigra. PD pathogenesis involves mitochondrial dysfunction, proteasome impairment, and alpha-synuclein aggregation, insults that may be especially toxic to oxidatively stressed cells including dopaminergic neurons. The enzyme methionine sulfoxide reductase A (MsrA) plays a critical role in the antioxidant response by repairing methionine-oxidized proteins and by participating in cycles of methionine oxidation and reduction that have the net effect of consuming reactive oxygen species. Here, we show that MsrA suppresses dopaminergic cell death and protein aggregation induced by the complex I inhibitor rotenone or mutant alpha-synuclein, but not by the proteasome inhibitor MG132. By comparing the effects of MsrA and the small-molecule antioxidants N-acetylcysteine and vitamin E, we provide evidence that MsrA protects against PD-related stresses primarily via methionine sulfoxide repair rather than by scavenging reactive oxygen species. We also demonstrate that MsrA efficiently reduces oxidized methionine residues in recombinant alpha-synuclein. These findings suggest that enhancing MsrA function may be a reasonable therapeutic strategy in PD.

Topics: Acetylcysteine; alpha-Synuclein; Animals; Antioxidants; Blotting, Western; Cell Death; Cells, Cultured; Cysteine Proteinase Inhibitors; Dopamine; Humans; Leupeptins; Mesencephalon; Methionine Sulfoxide Reductases; Mice; Neurons; Oxidation-Reduction; Oxidoreductases; Parkinson Disease; Rats; Rotenone; Uncoupling Agents; Vitamin E

Mutations in parkin and alpha-synuclein (alpha-syn) are linked to heritable forms of Parkinson's disease (PD). Recently, it has been shown that parkin mitigates alpha-syn-induced neuronal cell death in animal and tissue culture models, suggesting that there is a functional relationship between these two proteins. Although the mechanism by which parkin protects cells from alpha-syn-induced cytotoxicity remains elusive, it is tempting to speculate that parkin might directly regulate the normal metabolism and aggregation of alpha-syn. In the current study, we show that neither the suppression of endogenous parkin expression nor ectopic overexpression affects the steady-state levels of endogenous alpha-syn expression, overall aggregation of this protein, or breakdown of pre-formed aggregates in human neuroblastoma cells. These results suggest that parkin is not directly involved in the metabolism of alpha-syn, its aggregation, or the clearance of pre-formed aggregates.

Topics: alpha-Synuclein; Analysis of Variance; Blotting, Western; Cell Line, Tumor; Cysteine Proteinase Inhibitors; Gene Expression; Humans; Leupeptins; Neuroblastoma; RNA, Small Interfering; Transfection; Ubiquitin-Protein Ligases

Proteasomal dysfunction and alpha-synuclein (alpha-syn) have both been implicated in the pathogenesis of Parkinson's disease (PD). However, the functional relationship between these two remains elusive. Here we show that in human neuroblastoma cells, novel variants of alpha-syn with molecular weights of 22-25 kDa were induced after washout of the reversible proteasome inhibitors. Induction of these variants seemed to be a specific response to proteasome dysfunction, because the treatment and washout of other protease inhibitor or mitochondrial inhibitor did not induce these variants. Importantly, PD-linked alpha-syn mutations have effects on the formation of these variants. Recently, O-linked glycosylation and monoubiquitylation of alpha-syn have been reported. Despite the similarity in molecular weights, biochemical properties of our variants suggest that they are unrelated with such modifications. Taken together, these results suggest that alpha-syn is regulated by the specific functional state of the proteasomes, and PD-linked mutations may affect this regulation.

Topics: alpha-Synuclein; Glycosylation; Humans; Leupeptins; Parkinson Disease; Peptide Fragments; Proteasome Endopeptidase Complex; Recovery of Function; Ubiquitin

Parkinson's disease is characterized by dopaminergic neuronal death and the presence of Lewy bodies. alpha-Synuclein is a major component of Lewy bodies, but the process of its accumulation and its relationship to dopaminergic neuronal death has not been resolved. Although the pathogenesis has not been clarified, mitochondrial complex I is suppressed, and caspase-3 is activated in the affected midbrain. Here we report that a combination of 1-methyl-4-phenylpyridinium ion (MPP(+)) or rotenone and proteasome inhibition causes the appearance of alpha-synuclein-positive inclusion bodies. Unexpectedly, however, proteasome inhibition blocked MPP(+)- or rotenone-induced dopaminergic neuronal death. MPP(+) elevated proteasome activity, dephosphorylated mitogen-activating protein kinase (MAPK), and activated caspase-3. Proteasome inhibition reversed the MAPK dephosphorylation and blocked caspase-3 activation; the neuroprotection was blocked by a p42 and p44 MAPK kinase inhibitor. Thus, the proteasome plays an important role in both inclusion body formation and dopaminergic neuronal death but these processes form opposite sides on the proteasome regulation in this model.

Topics: 1-Methyl-4-phenylpyridinium; Acetylcysteine; alpha-Synuclein; Animals; Brain; Caspase 3; Caspase Inhibitors; Caspases; Cysteine Endopeptidases; Dopamine; Dopamine Agents; Dose-Response Relationship, Drug; Enzyme Inhibitors; Herbicides; Immunoblotting; Immunohistochemistry; Ions; L-Lactate Dehydrogenase; Leupeptins; Male; MAP Kinase Signaling System; Mitochondria; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; Multienzyme Complexes; Nerve Tissue Proteins; Neurons; Phosphorylation; Proteasome Endopeptidase Complex; Rats; Rats, Wistar; Rotenone; Synucleins; Time Factors; Ubiquitin

Dysfunction of the ubiquitin-proteasome system (UPS) has been implicated in Parkinson's disease (PD) and other neurodegenerative disorders. We have investigated the effect of UPS inhibition on the metabolism of alpha-synuclein (SYN) and parkin, two proteins genetically and histopathologically associated to PD. Pharmacological inhibition of proteasome induced accumulation of both parkin and SYN in transfected PC12 cells. We found that this effect was caused by increased protein synthesis rather than impairment of protein degradation, suggesting that inhibition of the UPS might lead to non-specific up-regulation of cytomegalovirus (CMV)-driven transcription. To investigate whether endogenous parkin and SYN can be substrate of the UPS, untransfected PC12 cells and primary mesencephalic neurones were exposed to proteasome inhibitors, and parkin and SYN expression was evaluated at both protein and mRNA level. Under these conditions, we found that proteasome inhibitors did not affect the level of endogenous parkin and SYN. However, we confirmed that dopaminergic neurones were selectively vulnerable to the toxicity of proteasome inhibitors. Our results indicate that studies involving the use of proteasome inhibitors, particularly those in which proteins are expressed from a heterologous promoter, are subjected to potential artefacts that need to be considered for the interpretation of the role of UPS in PD pathogenesis.

Topics: alpha-Synuclein; Animals; Cell Aggregation; Cysteine Endopeptidases; Humans; Leupeptins; Mesencephalon; Multienzyme Complexes; Nerve Tissue Proteins; Parkinson Disease; PC12 Cells; Proteasome Endopeptidase Complex; Rats; Rats, Sprague-Dawley; RNA, Messenger; Synucleins; Transfection; Ubiquitin-Protein Ligases

Parkinson's disease is characterized by loss of nigral dopaminergic neurons and the presence of cytoplasmic inclusions known as Lewy bodies. alpha-Synuclein and its interacting partner synphilin-1 are among constituent proteins in these aggregates. The presence of ubiquitin and proteasome subunits in these inclusions supports a role for this protein degradation pathway in the processing of proteins involved in this disease. To begin elucidating the kinetics of synphilin-1 in cells, we studied its degradation pathway in HEK293 cells that had been engineered to stably express FLAG-tagged synphilin-1. Pulse-chase experiments revealed that this protein is relatively stable with a half-life of about 16 h. Treatment with proteasome inhibitors resulted in attenuation of degradation and the accumulation of high molecular weight ubiquitinated synphilin-1 in immunoprecipitation/immunoblot experiments. Additionally, proteasome inhibitors stimulated the formation of peri-nuclear inclusions which were immunoreactive for synphilin-1, ubiquitin and alpha-synuclein. Cell viability studies revealed increased susceptibility of synphilin-1 over-expressing cells to proteasomal dysfunction. These observations indicate that synphilin-1 is ubiquitinated and degraded by the proteasome. Accumulation of ubiquitinated synphilin-1 due to impaired clearance results in its aggregation as peri-nuclear inclusions and in poor cell survival.

Topics: Acetylcysteine; alpha-Synuclein; Animals; Blotting, Western; Carrier Proteins; Cell Line; Cell Survival; Cysteine Endopeptidases; Cysteine Proteinase Inhibitors; Dimethyl Sulfoxide; Humans; Inclusion Bodies; Intracellular Signaling Peptides and Proteins; Kidney; Leupeptins; Macromolecular Substances; Mice; Multienzyme Complexes; Nerve Tissue Proteins; Neuroblastoma; Precipitin Tests; Proteasome Endopeptidase Complex; Protein Processing, Post-Translational; Synucleins; Transfection; Ubiquitin